從NMR弛緩研究探討蛇毒蛋白分子的動態行為

Dynamic Investigation of Snake Venom from NMR Relaxation Studies

李長欣(Chang-Shin Lee) ； 余靖(Chin Yu)

《化學》 55卷3期 (1997/06) Pp. 91-99

https://doi.org/10.6623/chem.1997037

摘要

臺灣眼鏡蛇(Naja naja atra)心臟毒蛋白II (cardiotoxin II: CTX II)是一個小分子量(6.8 kDa)鹼性的蛋白質，其二級結構全為β-板，它表現出多樣的生物性質。利用異核NMR實驗，研究CTX II的分子內動態行為，我們測量了在天然含量的α- ^(13)C之弛緩參數，它們包含了縱軸弛緩，橫向弛緩及異核^(13)C{^1H}NOE。弛緩的測量是在14.1T的NMR儀器上執行。動態數據的分析是使用Lipari & Szabo的無模型法則。它使用了次序參數( orde r parameter) S2描述分子內運動的振幅，有效相關時間(effectivecorrelation time)、描分子內運動的速度，及全轉動相關時間(overall correlation time)而描述分子滾動(tumbling)的速度。說們求出了50個^(13) C_α及三個threonine的支鏈^(13)C_α的運動參數。CTX II分子的τ_m為4.8 ns。動態研究與NMR結構計算的結果是一致的。位在三個環狀尖端的癌基，有相當的變動性。這些殘基的變動性對心臟毒與紅血球薄膜表面的“受體”結合，是相當重要的。在早先的預測lysine對心臟霉的溶血活性是重要的，我們的結果亦支持了此項推斷。

關鍵字

核磁共振 ； 弛緩 ； 骨架動態 ； 無模型法則

並列摘要

Cardiotoxin analogue II (CTX II) is an all ~-sheet, small molecu lar weight (6.8 kDa), basic protein possessing a wide array of biological properties. To characterize the internal dynamics of CTX II, longitudinal, transverse re laxation rates and heteronuclear ^(13)C{^1H} NOEs were measured for α -carbons at natural abundance by two-dimensional NMR spectroscopy. Relaxation measurements were obtained ina 14.1 Tesla spectrometer for 50 residues which are evenly spread along the CTX II polypeptide chain. Relaxation data were analyzed using the model free approach of Lipari and Szabo. he microdynamical parameters (S^2,τ_e and R_(ex)) were calculated with and overall rotational correlation time (τm) for the protein of 4.8 ns. The present study reveals that the functionally important residues located at the tips of the three loops are flexible and the flexibility of residues in this region could be important in the binding of cardiotoxins to their putative 'receptor s' which are postulated to be located on the erythrocyte membrane. In addition, the results obtained in the present study suppor t the earlier predictions on the relative role of the lysine residues in the erythrocyte lytic activity of cardiotoxins.

並列關鍵字

NMR ； Relaxati on ； Backbone Dynamics ； Model Free Formalism